Method for treating a mineral filler with a polydialkylsiloxane and a fatty acid, resulting hydrophobic fillers and uses thereof in polymers for breathable films

ABSTRACT

The invention relates to a method for treating a mineral filler by means of a polydialkylsiloxane and a fatty acid, the hydrophobic fillers thus obtained, and the application thereof in polymers for the manufacture of films and notably “breathable” films.

The present invention relates to the technical sector of treated mineralfillers, notably treated carbonates, notably calcium carbonates, and theapplications thereof in industry.

More particularly, the invention relates to the treatment of suchfillers with a view to making them hydrophobic and incorporating them inpolymers, for example for manufacturing films, notably “breathable”films, themselves incorporated for example in articles such asdisposable nappies and similar products.

In order to achieve industrial applications in the above fields, it isnecessary to produce mineral fillers, notably calcium carbonates, havingexcellent hydrophobicity and excellent repellency of water and aqueousfluids, and which can be mixed or “compounded” in appropriate polymers,generally polyolefins or mixtures or combinations of polyolefins.

So-called “breathable” films are well known to the skilled man in theart, in the aforementioned applications, as well as the propertiesrequired of them.

It is known notably that they must have a very good characteristic ofwater vapour transmission (which corresponds to their so-called“breathable” film characteristic). It is considered that theincorporated filler contributes, during a notably uni- or biaxialstretching, to the creation of micropores which increases thischaracteristic of “breathability”. The filler therefore has primeimportance in the final product obtained, and its properties.

In this light, the aspect ratio of the filler particle must be close to1 (ratio between length and mean diameter). The filler must not containcoarse particles, notably with a dimension greater than approximately 10micrometres, with a granulometry “top cut” of less than 10 micrometres,and the filler must contain only a small proportion of particles with anequivalent spherical diameter of less than 0.5 micrometres, that is tosay the BET specific surface area of the filler must be less than 6m²/g.

Naturally the treatments envisaged must be compatible with currentregulations.

It is also necessary, in almost all the applications to which this typeof product relates, for the incorporated filler not to impair thesuitability of the plastic film for being stretched or oriented uni- orbiaxially. It is also necessary, in order not to create predictabledosage problems during incorporation into the polymer, for theflowability properties of the filler to be good. It is also naturallynecessary for the filler to be able to mix easily with the polymer, andto disperse uniformly in the polymer matrix, failing which the finalfilm would be non-homogenous. During the incorporation of the polymer,the treated filler must not give off gaseous substances, which would inthe film result in areas which are cloudy and mechanicallynon-homogenous.

It is also necessary for the treatment not to affect the uniformity ofthe colour of the film obtained, that is to say to make it possible toobtain a film without mottling.

It can be seen that the problems and requirements related to thetreatment of such fillers are many and complex, and sometimescontradictory.

In the field in question calcium carbonates treated by means of stearicacid are known. For example, R. Rothon, “Particulate-Filled PolymerComposites”, Longman, Harlow, 1995, Ch. 4, will be cited.

Fillers are also known treated by means of silanes (E. P. Plueddemann,Silane Coupling Agents, Plenum Press, New York, 1982).

Fillers are also known which are treated by means of organopolysiloxaneswith H—SiO— bonds (patent EP 0 257 423) but which do not make itpossible to obtain fillers which can be used in the field of so-calledbreathable films.

Fillers are also known treated with stearic acid and then a siloxane,but in totally different applications.

However, current treatments with silane give rise to the release ofmethanol.

Thus the article “NMR Spectroscopic Investigations on the Hydrolysis ofFunctional Trialcoxysilanes” published in Zeitung für Naturforschung,54b, 155-164 (1999) describes a release of methanol.

The patent WO 99/61521 describes a carbonate treated on the surface inorder to obtain better hydrophobicity. The treatment employs stearicacid, as in the patent WO 99/28050.

The patent WO 96/26240 describes fillers flame retarded followingtreatment with fatty acid alone or with a fatty acid and a derivative ofsiloxane. The application sought is situated in the field in which thepolymers must have the property of non-flammability.

The patent JP 57 182 364 describes fillers used as facade coatings forconstruction materials, the said coating being impervious to water, andcontaining both a synthetic resin and a filler treated with aflame-retardant agent. The resins are derivatives of vinyl acetate oracrylate-vinyl acetate copolymers, which are not suitable for beingoriented uniaxially or biaxially, and which are not intended forbreathable films. The filler must have a very high granulometry, up to100 micrometres. The treatment exemplified is given for stearic acid andmethylcellulose, on an acrylic resin.

The patent WO 98/29481 is also known, which describes breathable filmsand which incorporates calcium carbonate as a filler. Reference can bemade to this document with regard to the generalities relating to thecharacteristics of the so-called breathable films. With regard to thefiller, the patent indicates only that it can be treated with a fattyacid, such as stearic or behenic acid, “in order to facilitate bulk flowand dispersion in the polymer matrix”.

The patent JP 52 39377 describes the use of stearin for preparingfillers, but in order to obtain better physical properties for the resinmatrix.

The patent WO 00/12434 describes the use of a desiccant, notably CaO,for preparing fillers for obtaining breathable films suitable to theuser.

The prior art devoted to breathable films has therefore used treatmentwith stearic acid or desiccant products of the CaO type. Stearic acidhas also been employed for treating fillers, but in totally differentapplications. A combination of fatty acid and silane has also been used.

No trend therefore stands out in the prior art, except for the treatmentof a filler with fatty acid alone or by the combination of fatty acidand silane in order to form a “coating”.

There therefore exists a constant search, and therefore a significantrecognised need, for the improvement of breathable films, and notablythe obtaining of films without mottling and without empty spaces as wellas for the improvement of the treated filler which such films contain.

The invention relates to a method for treating mineral fillers in orderto confer a hydrophobic character on them, making them suitable forbeing incorporated in polymers by means of which the so-called“breathable” films are produced, notably films of polyolefin(s),characterised in that a surface treatment of the filler is carried out,in two steps, the first step (pretreatment) comprising a treatment withat least one polydialkylsiloxane and the second step comprising atreatment with at least one fatty acid containing more than 10 carbonatoms, the two steps being able to be carried out simultaneously.

The invention therefore relates to a method for treating mineral fillersas described above, which surprisingly combines first of all apretreatment by means of a polydialkylsiloxane and then a treatment witha fatty acid such as stearic acid.

The combination of these two treatments, and in this order, results in aparticular set of properties, as demonstrated below, with a synergyeffect between the two treatment agents.

In practice, the polydialkylsiloxane will be added firstly and then thefatty acid immediately afterwards.

It is possible however in certain cases to effect the two additionssimultaneously, but taking care to ensure that the fatty acid nevercomes into contact first with the filler.

In general, it will be preferred to operate in two clearly distinctsteps, that is to say the addition of polydialkylsiloxane and then theaddition of fatty acid.

Throughout the remainder of the present application, the Applicanttherefore means, by treatment in two steps, a treatment in which theaddition of the two compounds takes place either in two steps separatein time, even with a short interval of time, or substantiallysimultaneously provided that the fatty acid does not come into contactwith the filler before the polydialkylsiloxane.

More particularly, the invention applies perfectly to natural calciumcarbonates such as marble and calcite or a mixture of them.

The invention also applies however to fillers such as precipitatedcalcium carbonate, talc, kaolin, magnesium hydroxide, various fillers ofthe type consisting of clay, silica, alumina, barium sulphate, mica,calcium oxide or hydroxide, aluminium oxides, mixtures thereof and thelike.

On the other hand, chalk does not give good results, which clearlyindicates that the probability of success of the invention was notabsolutely to be taken for granted.

According to a preferred embodiment, use is made of apolydialkylsiloxane of formula: (R)₃—Si—O—[(R)₂—Si—O—]_(n)—Si—(R)₃ whosealkyl group R is C1-C4.

In a particularly preferred manner, use is made of apolydimethylsiloxane (PDMS), for which the R group is the methylradical.

According to a preferred embodiment, use will be made of apolydimethylsiloxane with a kinematic viscosity of between 50 and100,000 centistokes (cSt), preferably between 300 cSt and 5000 cSt, verypreferably around 1000 cSt.

The best hydrophobicity is obtained between approximately 700 cSt and1300 cSt.

As a fatty acid, use can be made of any fatty acid having more than 10carbon atoms, and in an entirely preferred manner stearic acid, palmiticacid, behenic acid and mixtures thereof.

According to a preferred and naturally non-limitative embodiment, theimplementation of the method according to the invention is effected asfollows:

-   -   a high-speed mixer is used, in which the ground filler is        placed,    -   the polydialkylsiloxane is added at a temperature of around 100°        C., over 5 minutes, and, at the end of these 5 minutes,    -   the fatty acid is added.

It should be noted in this regard that polydialkylsiloxane has theadvantage of conferring nonstick properties on the mixture, which doesnot adhere to the walls of the mixer (but which adheres when nopolydialkylsiloxane is used).

The above method is preferably applicable to marble or calcite ormixtures thereof as a filler, to polydimethylsiloxane aspolydialkylsiloxane, and to stearin (a mixture of approximately 65%stearic acid and 35% palmitic acid) as a fatty acid having more than 10carbon atoms.

According to yet another preferred embodiment, use will be made of 100to 2000 ppm of polydialkylsiloxane by weight of dry filler, preferably200 to 1000, and in an entirely preferred manner around 500.

According to yet another preferred embodiment, use will be made of 0.6%to 1.4% fatty acid by dry weight of dry filler, preferably 0.8% to 1.2%.

The invention also relates to the above-cited fillers characterisedabove in that they have been treated by the method according to theinvention.

The invention more particularly relates to the fillers of this type,characterised in that they have high flowability, a BET specific surfacearea of between 2 and 6 m²/g and a granulometry top cut of less than 10micrometres, and preferably less than 8 micrometres.

By filler with a high flowability, the Applicant means a filler with anincline angle rate (rate between the incline angle rate of the treatedfiller and the incline rate of the non treated filler) determined by thefollowing method, called “pile method”, incline angle rate which is lessthan or equal to 0.98.

In practice, the determination of the incline angle representing theflowability of a powder is carried out by weighing 150 grams of thepowder. Then the powder is put in a 45 cm long vibratory feeder. Bysteady vibration of the feeder adjusted at level 8, the powder istransported ahead and put over the rim on the film, resulting in apowder pile, which is function of the filler. The incline angle α isthen calculated by tan α=Pile Height/Pile Radius.

The smaller the angle the better the flowability of the powder

The invention even more particularly relates to the said fillerscharacterised in that they have high hydrophobicity, that is to say inthat they have a turbidity index of between 0.9 and 1 and a foam indexof between 0.7 and 1, the two indices being determined by the methoddescribed below, referred to as the “whizzing method”, and in that theyhave a low moisture pickup, that is to say a moisture pickup less thanor equal to 0.42 mg/m² measured by the method described below andreferred to as the moisture pickup method.

In order to measure the hydrophobicity of the filler according to theinvention, the so-called whizzing method consists of introducing 0.5grams of the sample whose hydrophobicity it is wished to determine, intoa shaken test tube containing 3 ml of demineralised water. After 5seconds of stirring at 2000 rev/min, the turbidity, determined by meansof a UV and visible spectrometer, is calibrated between 0 and 1. Theturbidity index of 0 corresponds to a cloudy supernatant, the turbidityindex of 1 corresponds to clear water without any turbidity.

In a second step, there is added to the dilute sample 0.5 ml ofhydrochloric acid, with a concentration of 18% by weight, under stirringequal to 2000 rev/min for 5 seconds.

There then occurs a release of carbon dioxide due to the acid attack. Atone end of the calibration scale, a strong acid attack will then createa high release of carbon dioxide resulting in a high presence of foamcorresponding to a foam index of 0 and zero hydrophobicity whilst at theother end of the calibration scale a completely hydrophobic productcreates no release of carbon dioxide nor any foam, the foam index thenbeing one.

The method described below, referred to as the moisture pickup method,is based on the measurement of the increase in weight of the powderysample to be tested first of all placed, for 5 hours, in an atmospherewith a relative humidity of 10% and at room temperature, and then placedfor 2 hours in an atmosphere at a relative humidity of 90%.

Knowing the BET specific surface area of the sample tested, the quantityof water absorbed per unit surface in g/m² is then determined.

The invention also relates to all the applications of these treatedfillers in any sector of industry, notably the sectors where ahydrophobic character of the filler is required.

The fillers treated according to the invention can advantageously beincorporated in polyolefins, alone or in mixtures, the said polyolefinsbeing able to be chosen, non-limitatively, from amongst the following:low-density linear polyethylene, low-density polyethylene, high-densitypolyethylene and polypropylene and mixtures thereof.

The incorporation in the polyolefin or the appropriate mixture ofpolyolefins is effected in known equipment, and in a manner known to theskilled man in the art.

Likewise, reference can be made to WO 98/29481, dealing with the samegeneral application, for the manufacture of the breathable film withfiller, notably its uni- or biaxial stretching.

In fact, the invention also relates to a method for manufacturing aso-called “breathable” film of polyolefin(s), containing at least onemineral filler of the type mentioned above, and characterised in thatthe said filler has been treated by the method also described above.

According to the invention, master-batches or “compounds” are producedwhich contain 20% to 80% by weight of treated filler with respect to thetotal weight, preferably 45% to 60% by weight and particularlyapproximately 50% by weight.

According to a preferred embodiment, the said film undergoes a uni- orbiaxial stretching (or “orientation”).

The invention also relates to the articles containing at least one suchfilm, notably the products absorbing water or aqueous fluids such asdisposable nappies and similar products.

The manufacture of such products is well known to the skilled man in theart, as are the film stretching methods.

The invention also relates to the films thus obtained, in thenon-stretched or uni- or biaxially stretched state.

The invention also relates to the master-batches or “compounds” ofpolyolefin(s) and filler(s) treated according to the present invention,that is to say before putting in the form of a film.

The invention more particularly relates to the said master-batches or“compounds”, characterised in that they have a melt volume-flow rate(MVR) greater than 6 cm³/10 min (temperature 190° C., load 5 kg, diediameter 2.095 mm) measured according to ISO 1133 and a high thermalstability, that is to say a thermal stability expressed, according tothe followed method referred to as the strip method, by a length ofnon-discoloured strip greater than or equal to 20 cm.

The thermal stability determination method consists in putting thecompound in the form of a granule in an extruder in order to extrude abar. The said bar of compound is placed in an oven (Mathis Thermotester™sold by Werner Mathis AG) set at 220° C. As soon as the bar is placed inthe oven, it is moved towards the outside of the oven at a translationspeed of 0.833 mm/min.

Then the length of the bar where there is no change of colour isdetermined. The longer this length, the more thermally stable thecompound is.

Finally, the invention relates to the films themselves, containing atleast one filler treated according to the invention.

The invention more particularly relates to the said films, characterisedin that they are breathable films having a mottling index less than 10,measured according to the method described below and referred to as the“mottling viewer” method.

This mottling index is defined as a dimensionless number which measuresthe irregularities on the surface of the structure of the sample. A lowvalue of the mottling index indicates a surface with a very homogeneousstructure.

To do this, a sample (20 cm long, 15 cm wide and 20 micrometres thick)of the film to be tested is fixed, by means of an adhesive, to a sheetof black paper of DIN A4 format and with a mottling index of 2.01.

This sample thus prepared is placed in a colour scanner (PowerLook™ IIIfrom UMAX™ Systems GmbH) for acquiring the image data of the surface ofthe sample. It should be noted that the sample must first of all bedisplayed on a screen in order to select the region without folds, inorder not to falsify the results through an imperfect preparation of thesample.

The image data are then transmitted into a computer equipped with anSVGA graphics system and a PapEye™ image analyser from ONLY SolutionsGmbH in order to give the value of the mottling index.

The invention also relates to all the polyolefin articles containing atleast one such filler, even in a form other than a film.

The invention also relates to all the applications of these films andarticles, in any sector of industry, notably the sectors where ahydrophobic character of the filler and good redispersibility arerequired.

The invention will be better understood from a reading of the followingdescription, and the non-limitative examples below.

EXAMPLE 1

This example relates to the method for treating according to theinvention a marble with a mean diameter of 1.8 μm, with a top cut ofless than 8 μm and with a BET specific surface of area 4 m²/g for testsn° 1 to 7.

To do this, measurements are made, for the different tests of theexample and according to the aforementioned methods,

-   -   for the mineral filler, of the flowability, of the        hydrophobicity and the moisture pickup    -   for the compound, the MVR and the thermal stability    -   for the film, the mottling index.        Test N° 1

This test is a reference test using the untreated marble.

This untreated filler has an incline angle of 40°, a turbidity index of0, a foam index of 0, and a moisture pickup of 0.95 mg/m².

The master-batch or compound contains 50% by weight of the mineralfiller, 49.7% by weight of a linear low density polyethylene with an MVRof 15.4 cm³/10 min measured according to ISO 1133 and 0.3% by weight ofa thermal stabiliser.

The compound obtained has an MVR of 5.2 cm³/10 min and a lengthrepresenting the thermal stability of 10 cm. The film using the compoundobtained is prepared on a “cast film” production line.

The cylinder of the extruder has a temperature of around 240° C. to 250°C. and the stretching unit has a temperature of 80° C.

The speed of entry of the film on the first roller of the stretchingunit is 20 m/min, and the exit speed from the last roller of thestretching unit is 40 m/min.

The mottling index of the film obtained is 31.2.

Test N° 2

This test illustrates the prior art and uses a marble with a meandiameter of 1.8 μm, a top cut of less than 8 μm and a BET specificsurface area of 4 m²/g, treated by means of 1% by weight of stearin.

This treated filler has an incline angle of 45°, a turbidity index of 1,a foam index of 0.8 and a moisture pickup of 0.45 mg/m².

The master-batch or compound contains 50% by weight of the mineralfiller, 49.7% by weight of the same polymer as in Test N° 1 and 0.3% byweight of the same stabiliser as in Test N° 1, and has an MVR of 9.3cm³/10 min and a length representing the thermal stability of 23 cm.

The film using the compound obtained, prepared under the same operatingconditions and with the same equipment as in Test N° 1, has a mottlingindex of 21.1.

Test N° 3

This test illustrates a reference and uses the marble with a meandiameter of 1.8 μm, a top cut of less than 8 μm and a BET specificsurface area of 4 m²/g, treated by means of 500 ppm by weight of ahexadecyltrimethoxysilane.

This treated filler has a turbidity index of 0, a foam index of 0 and amoisture pickup of 0.88 mg/m².

The master-batch or compound contains 50% by weight of the mineralfiller, 49.7% by weight of the same polymer as in Test N° 1 and 0.3% byweight of the same stabiliser as in Test N° 1, and has an MVR of 6.2cm³/10 min and a length representing the thermal stability of 6 cm.

The film using the compound obtained, prepared under the same operatingconditions and with the same equipment as in Test N° 1, has a mottlingindex of 33.3.

Test N° 4

This test illustrates the prior art and uses the marble with a meandiameter of 1.8 μm, a top cut of less than 8 μm and a BET specificsurface area of 4 m²/g, treated by means first of all of 1% by weightstearin and then 500 ppm of the same silane as that used in the previoustest.

This treated filler has a turbidity index of 1, a foam index of 0.75 anda moisture pickup of 0.43 mg/m².

The master-batch or compound contains 50% by weight of the mineralfiller, 49.7% by weight of the same polymer as in Test N° 1 and 0.3% byweight of the same stabiliser as in Test N° 1, and has an MVR of 9.5cm³/10 min and a length representing the thermal stability of 23 cm.

The film using the compound obtained, prepared under the same operatingconditions and with the same equipment as in Test N° 1, has a mottlingindex of 21.0.

Test N° 5

This test illustrates a reference and uses the marble with a meandiameter of 1.8 μm, a top cut of less than 8 μm and a BET specificsurface area of 4 m²/g, treated by means of 500 ppm by weight ofpolydimethylsiloxane with a kinematic viscosity of 1000 cSt.

This treated filler has a turbidity index of 0, a foam index of 0 and amoisture pickup of 0.80 mg/m².

The master-batch or compound contains 50% by weight of the mineralfiller, 49.7% by weight of the same polymer as in Test N° 1 and 0.3% byweight of the same stabiliser as in Test N° 1, and has an MVR of 6.1cm³/10 min and a length representing the thermal stability of 6 cm.

The film using the compound obtained, prepared under the same operatingconditions and with the same equipment as in Test N° 1, has a mottlingindex of 29.7.

Test N° 6

This test illustrates the invention and uses the marble with a meandiameter of 1.8 μm, a top cut of less than 8 μm and a BET specificsurface area of 4 m²/g, treated first of all by means of 500 ppm ofpolydimethylsiloxane with a kinematic viscosity of 1000 cSt and then bymeans of 1% stearin.

This treated filler has an incline angle of 36° then a R rate of 0.9, aturbidity index of 1, a foam index of 0.8 and a moisture pickup of 0.39mg/m².

The master-batch or compound contains 50% by weight of the mineralfiller, 49.7% by weight of the same polymer as in Test N° 1 and 0.3% byweight of the same stabiliser as in Test N° 1, and has an MVR of 9.2cm³/10 min and a length representing the thermal stability of 23 cm.

The film using the compound obtained, prepared under the same operatingconditions and with the same equipment as in Test N° 1, has a mottlingindex of 7.6.

Test N° 7

This test illustrates the invention and uses the marble with a meandiameter of 1.8 μm, a top cut of less than 8 μm and a BET specificsurface area of 4 m²/g, treated by means of 500 ppm ofpolydimethylsiloxane with a kinematic viscosity of 1000 cSt, and bymeans of 1% stearin used simultaneously.

This treated filler has an incline angle of 36° then a R rate of 0.9, aturbidity index of 1, a foam index of 0.9 and a moisture pickup of 0.42mg/m².

The master-batch or compound contains 50% by weight of the mineralfiller, 49.7% by weight of the same polymer as in Test N° 1 and 0.3% byweight of the same stabiliser as in Test N° 1, and has an MVR of 9.4cm³/10 min and a length representing the thermal stability of 20 cm.

The film using the compound obtained, prepared under the same operatingconditions and with the same equipment as in Test N° 1, has a mottlingindex of 7.8.

Test N° 8

This test illustrates the invention and uses a marble with a meandiameter of 1.8 μm, a top cut of 10 μm and a BET specific surface areaof 2.4 m²/g, treated by means of 300 ppm of polydimethylsiloxane with akinematic viscosity of 1000 cSt, and by means of 0.6% stearin.

This treated filler has an incline angle of 34° then a R rate of 0.85, aturbidity index of 0.9, a foam index of 0.8 and a moisture pickup of0.42 mg/m².

The master-batch or compound contains 50% by weight of the mineralfiller, 49.7% by weight of the same polymer as in Test N° 1 and 0.3% byweight of the same stabiliser as in Test N° 1, and has an MVR of 9.7cm³/10 min and a length representing the thermal stability of 20 cm.

The film using the compound obtained, prepared under the same operatingconditions and with the same equipment as in Test N° 1, has a mottlingindex of 9.9.

Test N° 9

This test illustrates the invention and uses a precipitated calciumcarbonate with a mean diameter of 1.4 μm, a top cut of 7 μm and a BETspecific surface area of 5.3 m²/g, treated by means of 500 ppm ofpolydimethylsiloxane with a kinematic viscosity of 1000 cSt, and bymeans of 1.3% stearin.

This treated filler has an incline angle of 36° then a R rate of 0.9, aturbidity index of 0.95, a foam index of 0.9 and a moisture pickup of0.37 mg/m².

The master-batch or compound contains 50% by weight of the mineralfiller, 49.7% by weight of the same polymer as in Test N° 1 and 0.3% byweight of the same stabiliser as in Test N° 1, and has an MVR of 9.1cm³/10 min and a length representing the thermal stability of 22 cm.

The film using the compound obtained, prepared under the same operatingconditions and with the same equipment as in Test N° 1, has a mottlingindex of 9.1.

Test N° 10

This test illustrates the invention and uses a marble with a meandiameter of 1.8 μm, a top cut of less than 8 μm and a BET specificsurface area of 4 m²/g, treated by means of 500 ppm ofpolydimethylsiloxane with a kinematic viscosity of 1000 cSt, and bymeans of 1.2% behenic acid.

This treated filler has an incline angle of 36° then a R rate of 0.9, aturbidity index of 1, a foam index of 0.9 and a moisture pickup of 0.40mg/m².

The master-batch or compound contains 50% by weight of the mineralfiller, 49.7% by weight of the same polymer as in Test N° 1 and 0.3% byweight of the same stabiliser as in Test N° 1, and has an MVR of 9.2cm³/10 min and a length representing the thermal stability of 23 cm.

The film using the compound obtained, prepared under the same operatingconditions and with the same equipment as in Test N° 1, has a mottlingindex of 8.4.

It will be noted that Test N° 3 with a silane and without stearic acidproduces a high release of methanol (a quantity greater than 1500 ppmper volume), unlike Tests N° 6 to 10 according to the invention.

The same release of methanol is observed in Test N° 4, where stearicacid and a silane are combined.

The quantity of methanol released during the treatment is measured bymeans of a Dräger™ Tube 81 01 631 according to the instructions of usefrom the company Drager Sicherheitstechnik GmbH, Lubeck, Germany, ofNovember 1999 (5^(th) edition).

All the results obtained in these tests are set out in Table 1 below.

TABLE 1 Prior Prior Reference art Reference art Reference InventionInvention Invention Invention Invention TEST N⁰ 1 2 3 4 5 6 7 8 9 10Method Treatment — 1% 0.05% 1% 0.05% 0.05% 0.05% 0.03% 0.05% 0.05%stearin silane stearin + PDMS PDMS + PDMS + PDMS + PDMS + PDMS + 0.05%1% 1% 0.6% 1.3% 1.2% silane stearin stearin stearin stearin behenicsimulta- acid neously Filler “Whizzing method”: a) turbidity index 0.01.0 0.0 1.0 0.0 1.0 1.0 0.9 0.95 1.0 b) foam index 0.0 0.8 0.0 0.75 0.00.8 0.9 0.8 0.9 0.9 Humidity pickup mg/m² 0.95 0.45 0.88 0.43 0.80 0.390.42 0.42 0.37 0.40 Compound MVR (in cm³/10 min) 5.2 9.3 6.2 9.5 6.1 9.29.4 9.7 9.1 9.2 Thermal stability 10 23 6 23 6 23 20 20 22 23 (in cm)Film Mottling 31.2 21.1 33.3 21.0 29.7 7.6 7.8 9.9 9.1 8.4 index PDMS:Polydimethylsiloxane

A reading of Table 1 shows that only the tests according to theinvention lead both to films with a mottling index less than 10 and tofillers having a high hydrophobicity, that is to say a turbidity indexof between 0.9 and 1 and a foam index of between 0.7 and 1 and having alow moisture pickup, that is to say a moisture pickup less than 0.45mg/m² measured by the method described above, and also to master-batcheswith a volume fluidity index (MVR) greater than 9 cm³/10 min(temperature 190° C., load 5 kg, die diameter of 2.095 mm) measured inaccordance with ISO 1133 and a high thermal stability, that is to say athermal stability expressed, according to the above method, by a lengthof non-discoloured strip greater than or equal to 20 cm.

The invention also covers all the embodiments and all the applicationswhich will be directly accessible to the skilled man in the art from areading of the present application, from his own knowledge, and possiblyfrom simple routine tests.

1. A method for manufacturing a breathable film of polyolefin(s),comprising manufacturing said breathable film from a master-batchcomprising said polyolefin(s) and a mineral filler, wherein themaster-batch has a melt volume-flow rate greater than 9 cm³/10 min(temperature 190° C., load 5 kg, die diameter of 2.095 mm) measured inaccordance with ISO 1133 and a thermal stability expressed, according tothe strip method, by a length of non-discolored strip greater than orequal to 20 cm; and wherein the filler has been treated by a processcomprising a two-step surface treatment of the filler, wherein the firststep (pretreatment) comprises treating the filler with at least onepolydialkylsiloxane, and the second step comprises treating thepolydialkylsiloxane treated filler with at least one fatty acid havingmore than 10 carbon atoms, and the two steps can be carried outsimultaneously, the filler is selected from the group consisting ofmarble, calcite, precipitated calcium carbonate, talc, kaolin, magnesiumhydroxide, clays, silica, alumina, barium sulphate, mica, calcium oxideor hydroxide, aluminium oxide and mixtures thereof, and the filler has aturbidity index of between 0.9 and 1 and a foam index of between 0.7 and1, the two indices being determined by the whizzing method, and amoisture pickup less than or equal to 0.42 mg/m² measured by themoisture pickup method.